I'm just had my tooth out on the NHS. A few years ago, I had a… - Sally's Journal
I remember reading an article about some Dutch researchers who were studying populations of tits (no giggling there at the back) and identified two quite distinct behaviour patterns. Some tits were very bold and pushy, and others were very timid and nervous. It turned out that during times of dearth, the pushy tits did better (as measured in survival rates, I think), because they were willing to take more risks to get food, but during times of plenty survival rates were much higher amongst the paranoid tits, because the pushy ones got eaten by cats a lot.
Actually, that may be the wrong way round because my memory is rotten, but the observations neatly illustrated wryelle
's point about varying circumstances, and the population of the two behaviour patterns was largely stable over time.